> but what you need here is an ISP that handles IPv6 prefixes properly

It's hard to get ISPs to do things properly in general; if it's for IPv6, it's even more difficult. I think the intent of IPv6 designers was for hosts to manage to be prefix fluid; you might set up ULAs for local traffic, and use whatever prefixes are advertised for non-local traffic. Of course, that's harder to do than to write an RFC about, so I can understand resorting to prefix translation to get things done in the way desired. Prefix translation has the potential to be stateless which is nice for resource management on the translation element, though.